28nm Planar Flow

Device Context and Integration Logic

The AA N-free DARC Deposition step is inserted in the STI module after the formation of a multilayer hardmask stack consisting of pad nitride, inorganic hardmask, and an amorphous carbon layer, and before subsequent carbon/DARC repetitions and cap oxide deposition to form an optically and etch-balanced lithography stack for STI patterning [P2].At this point in the flow, the surface presented to lithography is dominated by carbon-based and dielectric har…

• [High] Residual Reflectivity and CD Swing: If the optical constants of the N‑free DARC drift due to composition or density variations, the intended destructive interference condition is not met, leading to incomplete reflectivity suppression and re-emergence of standing waves in the photoresist [P1].- [Medium] Interfacial Optical Mismatch with Carbon Hardmask: Chemical or structural incompatibility at the DARC/amorphous carbon interface can modify effective refractive index contrast, i…